In recent years, worldwide restrictions on exhaust gas are becoming tighter from the viewpoint of environmental protection.
Exhaust gas purification catalysts are being employed in internal combustion engines as one measure. In order to efficiently purify the hydrocarbons (hereunder abbreviated as “HC”), CO and nitrogen oxides in exhaust gas, exhaust gas purification catalysts employ a variety of catalysts, including platinum-group elements such as Pt, Pd and Rh, as catalyst components.
PTL 1 describes a method in which nitrogen oxides in exhaust gas are removed by contacting nitrogen oxide-containing exhaust gas with a catalyst containing platinum in the presence of hydrocarbons, in an oxidizing atmosphere (claim 1 of PTL 1).
PTL 2 describes an exhaust gas purification catalyst comprising a heat-resistant AlPO4 compound having a tridymite-type crystal structure and a BET specific surface area of 50-150 m2/g, and at least one type of precious metal component selected from the group consisting of Pt, Pd and Rh, supported on the AlPO4 compound (claim 1 of PTL 2).